To manufacture sheet-metal products of a predetermined shape by performing punching, bending, drawing, compressing and other types of machining on a sheet-metal blank, such as a steel sheet, the workpiece has heretofore been subjected to several processes. When a large quantity to sheet-metal products are involved, a means for performing several processes or stages in a single machining metal die by sequentially feeding the workpiece to the succeeding stages to complete the entire machining process in the final stage has been adopted. This type of multistage machining metal die, called the progressive die, has an advantage of high efficiency because one sheet-metal product can be produced with one stamping stroke of the press.
While the conventional type of progressive die, described above, has advantages of high production rates, short delivery time involved from the charging of a workpiece to the completion of machining, and less work in process, and volume production possible with a small number of workers, it has the following problems. The construction of the metal die becomes extremely complex because a plurality of punch-die sets are incorporated in a single metal die, requiring a high level of metal-die manufacturing technology. This leads to prolonged manufacturing time and increased manufacturing cost of each die.
To replace, repair the damaged metal die, and adjust part of the metal die, the entire metal! die has to be disassembled, involving troublesome work, and much time and labor accordingly. Furthermore, in a production system where a wide variety of products are manufactured in a small quantity, specially prepared metal dies have to be manufactured every time the shapes and sizes of workpieces are changed evenly slightly. This leads to increased metal-die cost, and makes it difficult to adapt to the so-called flexible manufacturing system (FMS) which has been increasing in need in recent years.